Carburetor for airplane engines



P 1947- J. F. CAMPBELL CARBURETOR FOR AIRPLANE ENGINES Filed Aug. 11, 1944 @511 I? Lmpiell INVENTOR.

each other. pilot operated throttle valve, and the fuel flow carburetors, the

Patented Sept. 23, 1947 CARBURETOR FOR AIRPLANE ENGINES John F. Campbell, Detro'it, Mich, 'assignor to George lV.[."'Holley and Earl Holley Application August 111, 1944,'Serial "No. 548,963

Claims. 1

The object of this invention is to control-1 the supply of 'fuel in an internal combustion engine (intended for use in an airplane) in proportion tothe weight of the air entering the engine. The specific object is to control the fuel air ratio when the throttle is first opened before the air flow is sufficiently great to make the .air venturi function, as the depression is :toofeeble at low air flows to operate the fuel air metering "means.

Fuel is usually supplied under pressure and the air and fuel flows are'measured. The air flow and the fuel'flow are then balanced against The air flow is controlled by 'the is automatically controlled so that it isin :pro-

portion to the air flow.

The air flow is measured by means of a venturi. When the air flow falls 70% below the capacity of the engine, the effective suction head then falls over 90%. Therefore, .at these low air flows, the metering becomes unreliable and the fuelsupply is regulated by a positive regulation of the fuel flow in proportion to the position of the throttle. Obviously, where'the throttle positively controls the position of the fuel restriction, the head on the restriction determines the flow.

The fuel is usually discharged into the air stream on the engine side of the air throttle.

In the operation of pressure-type airplane inevitable variations in the available fuel pressure haveintroduced-a small but significant error at these low air flows, and *as engines become larger these air flows are more important.

In addition, the variation in the downstream pressure of the fuel varies with the pressure at the point of discharge and the lower the downstream pressure, the greater the discharge, other things being equal.

As refinements have been introduced into-the art of metering fuel for such internal combustion engines, the desirability of eliminating these errors has become greater. Hence, the specific object is'to make these corrections.

The figure shows the preferred form of my invention when associated with an airplane carburetor, all to the left of the line XXbein drawn into which 'dip the impact tubes 14 and which a I passage 56.

2 connects with the diaphragm chamber 15 through l-fi is the diaphragm which forms the lower wall of the chamber I5 and the upper wall of the chamber 1, into which the depression created in 'thesmall venturi l8 'by-theair flow is introduced through a passage 55. The throat -of the venturi l8 is connected tothispassage 55 through a restriction 54.

In order -to compensate forchanges in air..1pressure and temperature, a partially exhausted capsule 50 in a chamber 5| in the air entrance v.Hl controls a -Valve-52. The chamber -,5l is at the air '1PI8SSUIB of the entering air as the passage 53 provides a free communication-between the chamber f5, and the chamber -l5' communicates with the chamber 13 through the t-passage 56.

"Fuel enters :at 20 "and -fiows through-a venturi 21, a depression corresponding to the square of the velocityof-theflow fof fu'el is created-in-the throat of venturi -21 and is communicated through passage 22 to the upper chamber 23,; chamber 25 located below chamber 23 communicates through the pipe 48 with the j'fuel .entrance 20.

A diaphragm 24 forms the bottom wall of the chamber 23 and the upper wall of the chamber 25. Hence, diaphragm "24 responds to the"pressure difference created bythe venturi 2|. A rod 26 connects the two diaphragms J6 :and -24 :together. Whentheiuel fiow=is such as to'giv'e the desired mixture ratio for that particular air flow, then the system'is imbalance and the rod :26 does not'move.

An oil pump 21, having ,a positive delivery, delivers-oil past the -valve-28on the end of the 'rod 26. At low airfiows a tension spring Q66 is provided-tohold'the valve '28 in-theopenposition. The valve 28 is provided withlan extensionsubjectedat its lower end to {the pressure i-inea cylinder 59 connected tothe return'oil pipe .34 through a pipe-58.

pressure relief valve fill is provided to limit :the maximum pressure developed by the oil =A restriction 41 ,permits a portion of the eoil pumped by pump 21 to return -to-the return pipe-4'5.

A pipe :3! delivers oil :to a chamber 1-4 berneath :a :piston 32. A spring 33 pushes the piston :32 downwards a fuel metering needle 35 .is :connected to the-piston 32- and regulates the ,flow :through \afuelmetering orifice 36. A reoturntpipe 34 connects the chamber iifi above the :piston :32 with the low ,pressure passage 45 for the oil pump 21. The valve 35 is guided concentrically by an extension 11.

A fuel discharge pipe 31 is provided with a fuel outlet valve 49 located on the engine side of the throttle II in the air passage [2.

A passage 38 communicates fuel pressure below the orifice 36 to the upper side of another piston 39. A passage 49 communicates the pressure above the orifice 36 to the lower side of piston 39. The piston 39 is provided with a notched opening 42 which forms a variable opening between a pipe 43 communicating with the outlet from the oil pump 21 and the pipe 44, which is connected through a restriction 46 with the low pressure side of the oil pump 21, which obtains its supply of oil from a supply tank not shown, which tank is at atmospheric pressure.

A pipe 51 connects the pipe 44 to the chamber in which the extension of the needle 35 slides.

A link 12 connected to a throttle lever 13 controls ,a valve 60. This valve Bil controls the flow of oil under pressure from the pipe 43 along a pipe 62 through a restriction 6|.

A pipe 54 conveys the oil flowing past the valve 60 to the chamber 65 and so back through the low pressure oil pipe 34 to the pipe 45. A cut-off valve 1| is located in the pipe 3|. A diaphragm 68 is connected to this pipe so as to close it when the diaphragm is moved to the right. A spring 69 engages with the diaphragm so as to move it to the left.

A chamber 10 is located to the right of the diaphragm 68 and. communicates with the low pressure oil'return line 34.

A chamber 15 is located to the left of the diaphragm 68 and communicates with the high pressure oil supply line 3 I A compression spring 69 is located in chamber 10 so as to engage with the diaphragm 68 and to Diameter of piston 32=% Rate of movement of spring 33:0.6" travel for. a pressure difference of 55 lbs. per square inch.'

Diameter of 35 (large) Diameter of 39 (piston) Rate of spring 4|=12 lbs. per inch.

Normal setting is based on 20 lbs. per square inch pressure drop between fuel entrance 20 and fuel exit 31.

Operation Assume the engine is running with the throttle open approximately 30. A depression is then created in the venturi l8 and communicated to the chamber I1, and the diaphragm I6 is thus drawn down by Venturi suction and the pump 21 is rotating at engine speed so as to create a pressure in the pipe 43 and in the hydraulic system generally. The needle valve 28 closes the orifice 29, the pressure in the pipe 3| falls, the piston 32 then responds to the compressed spring 33 and the valve 35 opens, admitting more fuel to the engine, that is, in sufiicient quantity to maintain the desired mixture ratio. If excessive fuel flow occurs, the diaphragm 24 moves up and checks the fuel flow by opening the valve 28 and increasing the pressure below the piston 32,.

The provision for compensation for changes in air density as influenced by the temperature and the pressure in the air entrance I is the valve 52. When the valve 52 moves down in re- .sponse to either high temperature or to low atmospheric pressure, the two chambers l and. I1

are placed in restricted communication with one another. Hence, the pressure difference between these two chambers is reduced and the fuel flow reduced.

When the throttle closes, the valve H is closed by the increase in pressure on the side of diaphragm 68, which is connected to chamber 14. This increase in the pressure difference is caused by the valve 28 opening as it does under low air flow. After the valve 1| is closed, the relation of fuel flow to throttle positions is empirical. By empirical, it is meant that the automatic control by the fluid flow responsive to fuel and air diaphragms ceases, and the control becomes positive and is taken over by the throttle movement. The valve 60 closes as the throttle closes. The valve 60 determines by its position the pressure difference above and below the piston 32. As the valve 30 closes, this pressure difference increases and the piston 32 rises and the valve 35 closes.

The pressure drop across the valve 35 however is the variable that must be eliminated when the throttle approaches its closed position; otherwise, the mixture ratio will vary with the pressure of the fuel entering the fuel venturi 2| at 2!]. Correction is obtained as follows: passage 38 applies high pressure fuel to a, piston 39, passage 40 applies low pressure fuel below the piston 39, hence, the piston 39 thus responds to the pressure difference between the entering fuel and the fuel discharged through passage 31 or more accurately to the pressure drop across the metering orifice 36. The spring 4| permits the valve 39 to move up and down in response to this pressure drop.

When the opening 42 closes due to a low pressure drop across the orifice 36, then the pressure in passages 57 and 44 falls to the pressure in the outlet passage 45 and the valve 35 moves down slightly to maintain the fuel flow in spite of a drop in fuel pressure in the entrance 20.

When the pressure drop across the orifice 36 becomes great, the piston 39 descends and the notch 42 opens and the pressure in 44 increases above the pressure in 45 due to the restriction 46 and the pressure in 44 increases; this increase is communicated below the valve 35 through the pipe 51 and the valve 35 rises, restricting the fuel flow and correcting for the increase in fuel pressure in the fuel entrance 20, which would otherwise introduce an error into the operation of the device.

The contoured notch 42 in the piston 39 thus acts as a valve and by-passes the fluid pressure created by the pump 21. Hence, when the drop across the metering orifice 36 is excessive, the pressure generated by the pump 21 is applied through passage 51 beneath themetering valve 35 to tend to restrict the fuel flow through orifice 36 past the valve 35 so that the mixture ratio is not influenced by the changes in the drop of pressure across the orifice 36.

It will be noticed that there is a circulation of air inside the chamber 5| and that the outside of the chamber 5| is subjected to the temperature of the incoming air so that the evacuated element 50 responds to both temperature and pressure. provided the element 50 is partly filled with air, nitrogen or some other gas. The pump 21 is preferably not driven by the engine so that'the revolutions of the pump 21 do not vary with the revolutions per minute of the engine. The oil in the pump 21 should have a pour point of at least F. a

When the throttle closes, the flow past the throttle l l with any given air density is determined within one or two per cent by the position of the throttle. A reduction of pressure below the throttle not giving any increase in air flow when the velocity past the lip of the throttle exceeds the critical, it follows that when the pressure drop at the lip of the throttle exceeds one half the available atmospheric pressure, air flow follows the throttle positions.

What I claim is:

1. In an airplane carburetor having automatic means for controlling fuel and air ratios when the throttle is partially and wholly open, means for controlling empirically the fuel and air ratio when the throttle approaches the closed position, comprising a positively driven oil pump adapted to be driven at a substantially constant revolution per minute and having an oil entrance and an oil exit, a source of fuel under pressure, a fuel control valve, means for moving said valve as the throttle is closed, comprising a cylinder, a piston therein, means for subjecting the opposite sides of the piston to the pressure differences created by said oil pump, yieldable means tending to open said valve, an oil pressure control valve connected to said throttle and adapted to control the pressure diiferences between the two sides of said piston, an oil passage connected to said oil pump, a piston valve therein adapted to respond to the pressure drop at said fuel valve and to regulate said oil pressure, means for applying the oil pressure as regulated by said automatic valve to move said fuel valve whereby as the fuel drop increases, the fuel valve is automatically closed to compensate for the increased fuel pressure drop,

2. In an airplane carburetor having automatic means for controlling fuel and air ratios when the throttle is partially and wholly Open, means for controlling empirically the fuel and air ratios when the throttle approaches the closed position, comprising a fuel passage, a fuel metering orifice and a cooperating movable regulating needle reciprocating therein, hydraulic means for moving said needle, means for generating pressure for said hydraulic means, means interconnected with the throttle for regulating said hydraulic pressure positively as the throttle closes, comprising a pressure pipe for the hydraulic fiuid, a valve in said pipe, said valve being mechanically connected to the throttle, a pressure release passage connected to said pressure pipe, an automatic valve in said release passage, yieldable means adapted to close said valve, means responsive to the pressure upstream of said fuel metering orifice to open said valve, means responsive to the pressure downstream of said fuel metering orifice to close said valve.

3. In an airplane carburetor having automatic means for controlling fuel and air ratios when the throttle is partially and wholly open, means for controlling empirically the fuel and air ratios when the throttle approaches the closed position, comprising a source of fuel supply under pressure, a fuel metering orifice, a tapered needle therefor having a cylindrical extension, the diameter of which is substantially equal to the diameter of said metering orifice, a cylinder having a piston connected to the other end of said needle, a spring means associated with said piston, a source of hydraulic pressure, means for applying said Pressure to the one side of said piston and to the cylindrical extension of the needle, a positively operated valve for regulating the hydraulic pressure difference on the opposite side of said piston, automatic means for regulating the pressure acting on the cylindrical extension, said automatic means being responsive to the pressure drop at said orifice, said positively operated valve being responsive to the closing movement of said throttle.

' 4. In an airplane carburetor having automatic means for controlling fuel and air ratios when the throttle is partially and wholly open, means for controlling empirically the fuel and air ratios when the throttle approaches the closed position, comprising a source of fuel supply under pressure, a fuel metering orifice, a tapered needle therefor having a cylindrical extension, a cylinder having a piston therein connected to the other end of said needle, yieldable means engaging with said needle, a source of hydraulic pressure, means adapted to apply a fraction of said pressure to one side of said piston, throttle controlled means for varying said first fraction, means for applying a second fraction of said pressure to said cylindrical extension of said needle, automatic means responsive to the pressure drop at said metering orifice for controlling said second fraction.

5. In an airplane carburetor having automatic means for controlling fuel and air ratios when the throttle is partially and wholly open, means for controlling empirically the fuel and air ratios when the throttle approaches the closed position, comprising a source of fuel supply under pressure, a fuel metering orifice, an air passage, a venturi therein, a throttle valve controlling the air flow, a fuel passage, a venturi therein, a first moving wall responsive to the pressure drop in said air venturi, a second moving wall responsive to the pressure drop in said fuel venturi, hydraulic means for regulating the fuel supply comprising a source of oil under pressure, a pressure regulating valve connected to both of said diaphragms whereby increasing differential air pressure tends to close said valve and increasing fuel pressure tends to open said valve, a fuel metering orifice in said fuel passage, a fuel metering valve therein, a third moving wall connected therewith,

means for applying hydraulic pressure to said third moving wall so as to close said metering valve, yieldable means for opposing said hydraulic pressure tending to open said fuel metering valve, means responsive to a high hydraulic pressure corresponding to low air and fuel fiows to close the connection from the hydraulic pressure to said third moving wall, means responsive to the closing movement of the throttle for applying hydraulic pressure to said third moving wall to empirically vary the fuel opening as the throttle approaches its idling position.

JOHN F. CAMPBELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,008,143 Mock July 16, 1935 2,281,411 Campbell Apr. ,28, 1942 2,234,001 Gistucci Mar, 4, 1941 2,269,294 Udale Jan. 6, 1942 2,095,233 Chandler Oct. 12, 1937 2,343,451 Garretson Mar. 7, 1944 2,361,228 Mock Oct. 24, 1944 

